Coffee has been consumed as a beverage for centuries. Over time, a wide variety of coffee-making methods and devices have been developed, e.g. percolators, vacuum pots, the “French press,” drip coffee makers, and others. During the first half of the 20th century, the espresso machine was developed in Italy. The principle of the espresso machine was to bring hot (but not boiling) water, under pressure, in contact with a quantity of finely ground, compressed coffee beans for a relatively short period of time, thereby producing one or two very small cups of highly flavored coffee.
The flavorful nature of espresso is mainly due to the layer of golden-colored crema floating at the top of the cup. The crema comprises emulsified oils and other substances extracted from the ground coffee beans by the pressurized water. Besides playing a key role in transmitting flavor, the crema layer has a visual appeal similar to that of a head on a glass of beer.
Other aspects of the espresso-making process that enhance the flavor are: 1) The hot water is in contact with the ground coffee for a relatively short time, long enough to extract flavor components but not so long as to damage them; and 2) Espresso is made as a single serving (or sometimes two servings), intended for immediate consumption, which prevents flavor components from degrading or evaporating.
These aspects of espresso-making are to be contrasted with other methods that involve the brewing of multi-cup quantities of coffee, which is then kept hot until consumed. Such methods typically require a longer period of contact between the ground coffee and the hot water, which can damage flavor components, and then some period of time between brewing and consumption, which can allow flavor components to degrade or escape through evaporation.
While existing methods of brewing coffee using espresso machines produce very flavorful coffee with an attractive crema layer, the coffee produced by such machines and processes is very thick and concentrated. Espresso as it emerges from the machine has been described as having the consistency of warm honey. The flavor is also very robust or strong. The quantity of coffee per cup is very small, on the order of one ounce. Because the quantity is small and the flavor volatile, it is usually consumed quickly, often while standing at a bar. This style of coffee is very much in favor in continental Europe, e.g. in France, Italy, and Spain, but is very different from the style of coffee chiefly favored in the United States.
While espresso consumption has increased markedly in the United States in recent decades, most coffee consumed in the United States is of a very different style, being less concentrated, less thick (less viscous), and less strongly flavored. Individual servings are also much larger, ranging from perhaps 6 to 20 ounces. Because this coffee is less concentrated and served in much larger quantity, different social rituals are associated with its consumption, compared to the quick consumption of espresso at a European espresso bar. In America, the large cups of low-concentration coffee are sipped over a relatively long period of time, for example as an accompaniment to a meal, or at a desk while working, or in a car while commuting.
In Europe, this style of coffee is called American Coffee and it is sometimes simulated by mixing together espresso and hot water. This, however, defeats the flavor preserving advantages of the normal espresso method and destroys the crema layer. At the same time, American tastes have become much more sophisticated, and many Americans, while continuing to prefer a large cup of coffee that can be sipped over time, would enjoy the visual appeal and flavor enhancement of a crema layer on the coffee. What is needed is a method for producing large servings of relatively low concentration coffee (i.e. American coffee) with some of the desirable characteristics of espresso, such as enhanced flavor and crema.